580 MONOGRAPHS OF NORTIT AMERICAN RODENTIA, 
which the close apposition of the ulna and -radius would indicate, the rela- 
tions of their various articular surfaces are the same as those in cases where 
pronation and supination are perfect, and such moyements are doubtless con- 
siderable in extent. 
Manus.—The carpals are nine in number, in two rows, four in the proximal 
and five in the distal series. The first bone of the proximal series, on the 
radial side, develops a large, flat, faleate process as long as the 1st meta- 
carpal, against which it lies; this process supports the outer one of the two 
large palmar tubercles at the radial side of the hand.* The second bone of 
this series, lunare if not scapholunare, is also of great size, irregularly semi- 
lunar in shape, with an oval convex facet, which forms most of the radio- 
carpal articulation. ‘The outer two bones are much smaller. In the distal 
row, one of the five bones is probably an ‘‘os intermedium”; this and three of 
the others are extremely small; the remaining larger bone is somewhat 
uncinate. 
There are five metacarpals, of which the 1st is much shorter than the rest, 
and directed obliquely away from them; the others are approximately parallel ; 
the ratio of their lengths is 3d, 4th, 2d, 5th, the last shortest. There is the 
normal number of phalanges—two in the pollex, three in each of the other 
digits. 
Pelvis—The sacral portion of the pelvis has already been described 
with the vertebrae. The pe/vis is rather long, narrow, and parallel-sided, about 
two and a half inches long from apex of ilia to the opposite extremity. The 
general axis of each innominate bone is straight. The ilia project about one- 
fourth of their length in advance of the sacrum (which terminates opposite the 
posterior border of the acetabula); their anterior prolongations embrace the 
whole of the last lumbar vertebra. The ilia are narrow trihedral bones, curving 
anteriorly outward, and somewhat clubbed at the extremity; the edges are 
all sharp, but the superior border is especially prominent; the outer surface 
is concave; the other two faces of the bone are flatter, the internal being 
roughened for the sacro-iliac synchondrosis. The shaft of the bone is con- 
stricted just above the acetabulum, though still markedly triangular in section. 
The acetabula are deeply cupped, surrounded by a prominent rim, except 
posteriorly, where the lip of the cup sinks into a deep notch. The ischial 
*In the Beaver, there is said to be a large “ accessory” carpal ossicle. It may be that the bone 
here described is the homologous ossicle of Haplodon, which, if substantiated, would furnish additional 
evidence of affinity between this genus and Castor. 
